Monday, May 17, 2010

The Green Sea Slug: An Animal With Photosynthesis

In his evolution apologetic, Science on Trial, Douglas Futuyma argued that the idea that the species were created is obviously false because they not well designed. Evolution, concluded Futuyma, must be true. For instance, Futuyma pointed out that photosynthesis is immensely useful, yet no higher animals have this mechanism. But new research is finding just that. The green sea slug, it seems, is part animal and part plant. As one report explained:

Pierce emphasized that this green slug goes far beyond animals such as corals that host live-in microbes that share the bounties of their photosynthesis. Most of those hosts tuck in the partner cells whole in crevices or pockets among host cells. Pierce’s slug, however, takes just parts of cells, the little green photosynthetic organelles called chloroplasts, from the algae it eats. The slug’s highly branched gut network engulfs these stolen bits and holds them inside slug cells.

Some related slugs also engulf chloroplasts but E. chlorotica alone preserves the organelles in working order for a whole slug lifetime of nearly a year. The slug readily sucks the innards out of algal filaments whenever they’re available, but in good light, multiple meals aren’t essential. Scientists have shown that once a young slug has slurped its first chloroplast meal from one of its few favored species of Vaucheria algae, the slug does not have to eat again for the rest of its life. All it has to do is sunbathe.

In fact the slug comes pre equipped with the necessary equipment to synthesize its own chlorophyll, the machine that captures energy from sunlight and makes plants green, and run the captured chloroplasts. As one researcher put it, “This could be a fusion of a plant and an animal—that’s just cool.” It certainly is, and for evolution it is bizarre. As one evolutionist put it, “Steps in evolution can be more creative than I ever imagined.”

Another example of how evolution can support nearly any finding. Its findings make it so settled that the fact of evolution is beyond doubt except by loons. Of course as the findings change evolution becomes even more settled because of the great creativity it employs.

1) "Futuyma pointed out that photosynthesis is immensely useful, yet no higher animals have this mechanism."

And these slugs don't. They steal that ability from algae, whose chloroplasts they retain. A slug, raised in the lab without algae, cannot execute photosynthesis.

Similarly, ruminants can't digest cellulose without bacteria. Storing and using other organisms is common- and even human gut bacteria provide calories and vitamins.

2) Horozontal gene transfer is not a falsification of evolution, nor evidence for design. If anything, this work yields support to endosymbiont theory. Horozontal gene transfer is being argued by the scientist, and is the explination for what you, I guess, willfully overinterpret as design: "pre equipped with the necessary equipment."

3) What, therefore, is the design in the system? What detection method or calculation did you use? How does it distinguish design from non-design, and at what confidence level?

4) Considering this blog spends a lot of time jumping on scientists for overstating conclusions, it is interesting you have re-reported unpublished data from a meeting as reported by wired. Even that aricle warns:

"Zardus, who says that he tries to maintain healthy skepticism as a matter of principle, would like to hear more about how the team controlled for algal contamination."

Algae and plants don't 'make' chloroplasts-they and mitochondria are self-replicating endosymbionts with their own genome.

A lot of functionality in chloroplast and mitochondrial genomes has been lost, and transferred to nuclear (host) DNA.

Plants, for example, make chlorophyll, and proteins, and supply it to chloroplasts.

These slugs eat algae and store the chloroplasts. They also get a heavy dose of algae DNA in the process. At some point, key genes may have been incorporated (not sure this has been proven-the reference Dr. Hunter provides certainly doesn't demonstrate it) and expressed. This would have been advantageous, because the chloroplasts would then persist for life, and the slug wouldn't have to keep eating them every few days, or weeks, or however long an unsupported chloroplast keeps working outside the algae.

Bacteria are, by far, the best at horizontal gene transfer. Some even sample there environment with DNA 'pumps' that pull anything they find in. They then give it a try.

Makes sense-an organism enters an environment, and samples the genes that the locals are using to survive. Then they steal that ability, in some cases, poison them, and win. Acinetobacter, in particular comes to mind.

"So the sea slugs deveped the ability to recycle chloroplasts and make chlorophyll at the same time? "

Not necessarily, and I don't get that this is what is being proposed.

Some chloroplasts, including these, are stable for days to weeks*. They are loaded up with what they need, by the algae, and good to go for some time. So, sea Slugs could have been using them by harvesting them as needed prior to an HGT event. (In fact, a quick search turned up that some seem to do this, and need to replenish often). Slugs that acquired the ability to sustain the chloroplast through HGT would have a huge advantage in not having to continually harvest algae. They are set for life, after their first meal.

And they somehow learned how to not get digested in the slug's digestive system, and somehow find thier way to the right spot on the slug's body to catch the sunlight. This puts me in mind of some of the "Just So" stories.

Is there a day that goes by on this blog where a creationist doesn't casually accuse someone of creating/reciting a 'just-so' story?

This is an intellectually lazy appeal to incredulity. Rather than honestly investigating what might be happening, the approach is simply to say "that's a 'just-so' story" and prove it by inserting the word 'somehow' gratuitously into the paragraph to show just how implausible the scenario must be.

This seems especially true when my response is a perfectly good hypothesis countering a "that seems somehow weird therefore, design" argument. The hypothesis implies stepwise evolution, , references known natural mechanisms, etc. Sure the details need to be worked out, and certainly, it could be false.

But that's the difference between ID and science. We'd continue to inquire into the nature of the system. Natch et al. already have the answer: it is designed/created that way. Case closed.

Btw, no one has answered how they've detected design in this slug (or any other) system on this blog.

Evolution may be true, but that would be awfully strange. One thing that is clear is that it is not a fact, as evolutionists insist. Instead, this is a clear sign of metaphysics infecting science. Like the Wizard shouting down Dorothy.

The question of how the green sea slug got its abilities to implement photosynthesis, or of a million other designs in biology, is underdetermined. We don't know how these arose. That is the relevant scientific fact here. And any scientist who won't say that loud and clear is is guilty of misrepresentation. This is not skepticism, this is realism.

HGT doesn't break the nested hierarchy. It does complicate its detection. If we did a phylogeny of these algal genes in slugs, we'd see the genes would appear related to algae. The rest of the slug genome would look slug-ish. This is one way HGT can be detected, and modeled. Papers like the one in the preceding blog entry, and the following use sophisticated algorithms to detect and model HGT along with vertical inheritance.

"...However, recent studies indicate that the species tree and the hierarchical classification based on it are still meaningful concepts, and that state-of-the-art phylogenetic inference methods are able to provide reliable estimates of the species tree to the benefit of taxonomy. Conversely, we suspect that the current lack of completely sequenced genomes for many of the major lineages of prokaryotes and for most type strains is a major obstacle in progress towards a genome-based classification of microorganisms. We conclude that phylogeny-driven microbial genome sequencing projects such as the Genomic Encyclopaedia of Archaea and Bacteria (GEBA) project are likely to rectify this situation."

"HGT doesn't break the nested hierarchy. It does complicate its detection. If we did a phylogeny of these algal genes in slugs, we'd see the genes would appear related to algae. The rest of the slug genome would look slug-ish."

But then, how do you can be sure about a UCLA? For example catharrhine and platyrrhine monkeys may have descendended not from a common ancestor but from ancestor that had horizontal transferred genes and then evolved convergently.Or you have a prove that it not happened?

You could start by trying to see if even a single case of HGT between two animals have been documented. Then you can ask yourself if vertical gene transfer would be more likely than HGT in this specific case.

Cornelius G. Hunter is a graduate of the University of Illinois where
he earned a Ph.D. in Biophysics and Computational Biology. He is
Adjunct Professor at Biola University and author of the award-winning Darwin’s God: Evolution and the Problem of Evil. Hunter’s other books include Darwin’s Proof, and his newest book Science’s Blind Spot
(Baker/Brazos Press). Dr. Hunter's interest in the theory of evolution
involves the historical and theological, as well as scientific, aspects
of the theory. His website is http://www.darwins-god.blogspot.com/